Nucleation of Manganese Oxides in the Presence of Reactive Halogen Species

由美国国家科学基金会化学部环境化学科学项目资助的华盛顿大学教授Jun Young-Shin正在研究盐水中氧化锰颗粒的形成。锰氧化物在环境中含量丰富，在去除污染物方面具有重要作用。它们的形成可能受到人类活动中含有高浓度盐的产物的影响，例如海水淡化和油气开采。所涉及的化学反应知之甚少，包括卤化物离子（如氯化物和溴化物）和高活性卤素的作用。这项工作定量和定性地研究了海水化学如何影响环境中锰氧化物的形成。该项目还为代表性不足或经济状况不佳的K-12学生制定了环境化学推广计划。这种拓展既鼓励高中生和本科生尽早参与研究，又通过纳入研究成果来改善大学课程。从水和能源生产过程中产生的高盐废水的增加提出了它们对环境影响的问题。特别是，卤水中的卤化物可以极大地影响天然水生系统中矿物的形成和溶解过程。在阳光照射下，卤化物进一步发生光化学反应，生成活性自由基。然而，在日光照射下卤化物对氧化还原活性过渡金属离子及其固相形成的影响尚不清楚。本项目研究了活性卤素对水中锰离子氧化的影响，以及在有和没有天然有机物的情况下锰颗粒成核和生长的动力学。假设天然有机物质与卤化物在光解过程中产生的活性物质可以促进Mn2+ (aq)的光化学氧化，促进锰氧化物的高氧化态的形成。为了阐明新形成的锰氧化物的性质和考察其动态氧化还原反应行为，对锰氧化物的固相和流体化学进行了表征。基于原位同步加速器的小角度x射线散射提供了锰氧化物成核和生长的实时信息。该项目推进了关于高盐体系中锰氧化物成核机制和动力学的基础知识，这对于预测污染物的去除和运输以及开发新的锰基材料非常重要。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Funded by the Environmental Chemical Sciences Program of the NSF Division of Chemistry, Professor Young-Shin Jun at Washington University examines the formation of manganese oxide particles in salt water. Manganese oxides are environmentally abundant and are important in removing contaminants. Their formation can be affected by products from human activities that have high salt concentrations, such as from desalination and oil and gas recovery. The chemical reactions involved are poorly understood, including the roles of halide ions (e.g., chloride and bromide) and highly reactive halogen species. This work quantitatively and qualitatively examines how salt water chemistry affects the formation of manganese oxides in the environment. The project also develops environmental chemistry outreach programs for underrepresented or economically disadvantaged K-12 students. This outreach both encourages the early involvement of high school and undergraduate students in research and improves university courses by incorporating research outcomes.The increased production of highly saline effluents from water and energy generating processes raises questions about their impacts on the environment. In particular, halides in brine can greatly affect mineral formation and dissolution processes in natural aquatic systems. With sunlight, halides may further undergo photochemical reaction to generate reactive radical species. However, the effects of halides under sunlight exposure on redox-active transition metal ions and their solid phase formation are still obscure. This project investigates the effects of reactive halogen species on the oxidation of aqueous manganese (Mn) ions and the kinetics of the nucleation and growth of Mn particles, with and without natural organic matter. It is hypothesized that reactive species generated from reactions between natural organic matter and halides during their photolysis can promote the photochemical oxidation of Mn2+ (aq) and facilitate the formation of higher oxidation states of manganese oxides. To elucidate the properties of newly formed manganese oxides and to examine these dynamic redox reaction behaviors, solid phases of manganese oxides and fluid chemistries are characterized. In situ synchrotron-based small angle x-ray scattering provides real-time information about the nucleation and growth of manganese oxides. The project advances fundamental knowledge regarding the nucleation mechanisms and kinetics of manganese oxides in highly saline systems, which is important for predicting contaminant removal and transport and for developing new manganese-based materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.